The present invention relates to a process for improving granular detergents. To be more precise, it relates to a process for reducing the quantity of water-insoluble substances which would adhere to the wash at the time of washing with a granular detergent containing anionic surface active agent, alkali metal silicate and alkali metal carbonate, which process involves surface treatment of said granular detergent.
Ever since it was pointed out that phosphates which had been prevalently employed as inorganic builder for granular detergents cause environmental pollution, the work of reducing the phosphorus content of granular detergents has been positively undertaken in the detergent manufacturing industry. As an art of minimizing the phosphorus content from this point of view, there is known the art of employing silicate and carbonate of an alkali metal jointly as inorganic builder and reducing the quantity of the alkali metal phosphate to be employed. There have been developed several granular detergents with low phosphorus content embodying this art.
However, inasmuch as the alkali metal silicate has a reactivity with carbonic acid gas to form water-insoluble substances, these granular detergents tend to absorb carbonic acid gas from the air while in storage, for instance, and to form water-insoluble substances within the detergents. When water-insoluble substances are thus formed, they not only impair the detergency of the granular detergent per se, but also they adhere to the fabrics washed with the detergent, thereby causing the commercial value of the granular detergent to be reduced.